This invention relates to new and useful improvements in lock assemblies. The integrity of conventional self-latching or self-locking lock assemblies is easily breached either by sliding a flexible sheet against the curved portion of the latch or by spreading the door jamb from the door edge with a crowbar or the like. These are the two main methods of forcing a lock and it is therefore normal to provide an additional dead bolt on the door for extra security.
However, dead bolts require separate keys and a separate opening and closing action and furthermore, they are not self-locking when the door is closed.
Attempts have been made in the past to overcome these disadvantages and prior art known to the applicant includes the following patents:
U.S. Pat. No. 2,136,408 PA1 U.S. Pat. No. 2,217,098 PA1 U.S. Pat. No. 2,344,532 PA1 U.S. Pat. No. 2,889,164 PA1 U.S. Pat. No. 3,116,082 PA1 U.S. Pat. No. 3,691,799
However, all of these suffer from several disadvantages inasmuch as they are sometimes easily breached and where not easily breachable, are relatively involved so that they become expensive to construct.
Furthermore, none of them are adaptable for use with a conventional locking set but have to be manufactured in their entirety.